This is my code:
class bla:
def function1():
print 1
def function2():
bla.function1()
x = bla()
x.function2()
I don't understand why I get the error "TypeError: function2() takes no arguments (1 given)" as I don't seem to be passing any argument to function2.
Regular methods are called with an implicit self reference to their object - otherwise they wouldn't be able to access any data members of x.
They should always be declared like so:
class bla:
def function1(self):
print 1
if you want them to operate on the object (self is loosely equivalent to the this pointer in C++, for example).
Alternatively, if you don't care about the object (so you're really just using the class to group some functions together), you can make them static like so:
class bla:
@staticmethod
def function1():
print 1
@staticmethod
def function2():
bla.function1()
In fact, that's the only way you can call bla.function1() without an instance of bla from your function2.
That's cause your calling your function as a method and that automatically binds the method's object as the first argument to your function.
Either do:
bla.function2() #a function call
or:
class bla:
#normal and correct way to define class methods - first argument is the object on which the method was called
def function1(self):
print 1
def function2(self):
self.function1()
You have to type:
class bla:
def function1(self):
print 1
def function2(self):
self.function1()
self (a reference to the object on which the method is called) is passed as the first parameter to each method. The name of this first variable, "self" is just a common convention.
You have to pass the argument self to the functions function1 and function2. See the Python Classes documentation. So your code would be
class Bla: # Notice capitalization.
def function1(self):
print 1
def function2(self):
bla.function1()
x = Bla()
x.function2()
See also the answers to the question Why do you need explicitly have the “self” argument into a Python method?.
Basically in Python a call to a member function (like function1)
x = Bla()
x.function1()
is translated into
Bla.function(x)
self is used to refer to the instance of the class x.
